Dimension gauge



2, w46. J. B.' HALL 24i087'7 DIMENSION GAUGE Filed Aug. 27, 194s i 2sheets-sheet 2 Iaweazoal: da.. 6M

Patented Nov. 12, 1946 DIMENSION GAUGE JohnB. Hall, Wakefield, Mass.,vassignor of onehalf to Frank I. Hardy, Boston, Mass.

Application August 27, 1943, Serial No., 500,269

3 Claims.

This invention relates to improvements in tools and more especially toimprovements in gauges of the type employed in making precisionmeasurements whereby mechanical parts are brought into close conformancewith accepted standards;

Examples of precision tools of the character rem ferred to are surfaceplates, snap gauges, plug gauges, angle irons, pedestals, and manyothers. Thesetools are customarily made of metal, a ma,- terial which issubject to the development of. lnaccuracies` from Various causes. Forinstance, metal develops dimensional instability upon exposure toiiuctuating temperature conditions. Similarly, metal is subject tominute distortion or flexing from pressure conditions developingexternally of the metal, as by a. weight applied thereon, and alsointernally of the metal from stresses and strains within the metalitself. Gauges of metal are further subject to Wear which likewisecauses inaccuracies. In the case of some of these tools, as for instancesurface plates,` it is necessary t provide relatively large surfacesnnished to a line tolerance. Such surfaces cannot be accurately formedby conventional grinding operationsand as a result, hand scrapingoperations are necessary which require considerable time and' greatlyincrease the cost of the tool.

An object of the invention is to improve tools used in making precisionmeasurements and to devise means for overcoming er substantiallyreducing the various difliculties above noted. a further object of theinvention to. provide irnproved gauges which are characterized bycheap.- ness, durability, and more ecient operation.

The nature of the invention and its objeetswill.

be more fully understood from the following. de-

scription of the drawings, and discussion relating.

thereto.

In the accompanying drawings:

Fig. l is a perspective view illustrating a surface plate of theinvention;

Fig. 2 is a cross section taken on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged detailed view of the surface plate illustrating aground surface;

Fig. 4 is a perspective View illustrating a modi-V It isv selvestoformation into various types of precision tools, inV which form therocks provide various advantages in comparison with metal. Examples ofmaterials suitable for this purpose are the igneous rocks, suchasgranite, gabbro, diorite, dabase, basalt, trap, rhyolite, and others.

Theterm igneous rock as employed in geology ief'ersto a class-'ofsubstances which were formed by heat beneath the earths crust and forcedto thel surface by pressure, thereafter forming an extremely hard massthrough a period of slow cooling and seasoning. Igneous rock of theclass represented by the above indicated group of rocks, du@ tov slowcooling and seasoning processes, is substantially free from stresses andstrains such are sometimes encountered in metal, is substantiallyunaffected by temperature changes, and is highly incompressible. Igneousrock is distinguished fromK sedimentary rock by the fact that the lattersubstance is formed by deposits in thelabsence of heat.

There occur in nature several'types of granite which are, furtherclassied as biotites, hornblend, biotite-muscovite, andquartz-monzonite, andthe like. Ofthese; the largest number of so-Calledcommercial granites. utilized in connection wit the invention, arebiotites.

Referring more in, detail to the application of igneous rock toprecision tools, I have disclosed in Fig. l' a preferred embodiment ofthe invention, consisting of a surface plate I which is composedentirely of a granite such as biotite. The surface plateco-nsists of aflat slab of the granite. To facilitate handling, the granite may, ifdesired, be formed with rib portions 2 and with a flange or overhanging,edge 3 constituting an extension ofthe workingV surface il. The surface4 presents a grain formation made up of tiny peaks 5 and.

pits or depressions 6.

characteristic of the granites is a well-dened grainV formation whichmay be visualized as resulting from multiplicity of tiny flat particlespiled one upon another in a definite pattern of straight lines. Cleavageof the rock across. the particles forms a definite grain surface, whichis commonly, referred. to as the head grain, and a surface` formed b ycleaving a granite body across its particles includes the characteristicheads 5 and pits 5, illustrated in Fig. 3 of the drawings.

The importance of the grained surface l of the plate l is bestunderstood from a consideration of thek requirements of a conventionalsurface plate; Such tools are generally utilized to provide an extremelyaccurate supporting surface for assembling work which must be finishedto close tolerance (.0001-.0005). Such a requirement calls for anexceedingly smoothly finished surface which, in the case of metal, mayreduce slidability. In the case of a surface plate especially, it isdesired to maintain slidability at the surface so that work may beeasily adjusted and will not freeze thereon. To prevent such freezingwhile still maintaining ne tolerance, it is customary to hand scrape ametal surface and form therein minute depressions which serve to preventfreezing.

The grained surface 4 of the granite surface plate of the invention isespecially desirable from the slidability point of view since by reasonof the tiny pits E occurring between the heads 5, an interrupted surfaceis always provided for and "freezing is automatically avoided.

In place of the hand scraping operation commonly carried out on metal,the present plate is surfaced by a grinding operation, utilizing granitesurfaces which are applied to the surface tc be ground, in conjunctionwith the use of a fine abrasive such as carborundum. While the surface 4is preferably formed from cleaving the granite across the grain toexpose the head grain in the manner described, it may nevertheless bedesired, for some types of tools, to utilize the granite with the grainrunning in other directions than at right angles to the plane of thesurface of the plate.

Formation of a metal surface by hand scraping operations is a diicultand time-consuming operation, made necessary by reason of the fact thatmetal grinding equipment cannot be used on account of deflection ordistortion developing in the grinding members. In the case of thegranite plate, however, surface grinding operations may be successfullycarried out by the use of granite grinding members which are not subjectto deflection or other dimensional instability.

Grinding may be carried out by reciprocating movement of a granite blockon a plate surface, making use of abrasive such as carborundum, or bygrinding with a granite wheel, or in other ways. One immediate resultobtained from this ability of granite to serve as a grinding member asWell as to be formed by grinding, is that close tolerances can becarried out on relatively large sized plates, whereas it is practicallyimpossible to conform to standard tolerances by hand scraping of metalin the larger sizes of surface plates. For example, a tolerance of .0001of an inch is commonly specified for a 12 square metal plate, while a24" square plate can only beground to .0002 tolerance and so on, withlarger sizes being limited to tolerances of .001 or greater. With theplate of the invention, a .0001 tolerance can be maintained throughoutthe surface of large size plates.

In use, the granite surface plate exhibits several unusual properties.It is substantially free from dimensional changes in the presence offluctuating temperatures, and it is believed that if any change whateverdoes take place from changing temperature conditions, it does so in avery uniform manner, with the result that no irregularities develop inthe surface 4 of the plate. This resistance of the granite totemperature changes is thought to be due in part to the fact that it isof a highly impermeable and seasoned character and that it only veryslowly accepts or releases heat. Because of this dimensional stabilityit is possible to provide standard gauge members, in

various sizes, which may be used in a wide range of temperatures withoutsignificant variation ln tolerance.

A common feature of metal surface plates is a reinforcing constructionconsisting of a number of ribs disposed at the under side of the metalsurface plate and running in various directions to offset any deflectionin the plate from pressure conditions. Such deflection is generallyrecognized as being due to a slight resiliency present in metals,especially those which may include stresses and strains.

The matter of deection in the case of the granite surface plate of theinvention does not arise since there is substantially no resiliencewhatever in the granite and it develops no tendency to flex under anypressure conditions, due to its highly incompressible mass formed underheat and pressure and subsequent slow cooling by natural processes.

The tendency of metal surface plates to Wear, results in the need forfrequent correction and resurfacing operations of expensive character.This problem of Wear is greatly minimized by the use of granite as thelatter material successfully withstands usage with a highly developedresistance to wear which has not been fully determined but which isunderstood to greatly reduce resurfacing operations, and in some casesto eliminate resurfacing throughout the life of the tool.

The surface plate of the invention is characterized by various otheradvantages such as being rust and corrosion resistant, and hence doesnot require applications of oil or grease to protect the finishedsurface. The surface itself can be renished in less time and at lesscost than is the case with metal. The finished granite surface whendamaged will not raise burred edges, which might scratch or mar lappedmetal surfaces applied thereon. Instead of raising burred edges, thesurface plate merely chips away, leaving only a depression.

The dimensional stability of granite and other i igneous rocks furnishesa basis for a desirable modification of the conventional form of surfaceplate. Such a modification has been illustrated in Fig. 4. I have chosento designate the modification as a table gauge. This gauge includes abase 'l consisting of a granite surface plate corresponding in allrespects to the surface plate I illustrated in Fig. 1. Mounted on thebase 'l is an upright frame member 8, also composed of an igneous rocksuch as granite, and preferably formed with a side surface 9 whichextends at right angles to the plane of the surface l0 on the surfaceplate 1, thus to provide a second vertical gauge surface of equaldimensional stability and ne tolerance. In addition, the frame has a topanvil portion Il, with still a third gauging surface I2 formed at theunder side thereof, which lies in a plane parallel with the surface I0.The distance between the surfaces is carefully ground to a standard,thus to provide in effect a greatly enlarged snap gauge which includes asurface plate of a size adapted for large scale work.

The modification illustrated by Fig.. 4 may further include an angleiron member i3, having still another gauging surface B4 which extends atright angles to the plane of the surface l0 and parallel with thesurface 9 of the upright frame 8. The angle iron i3 is illustrative ofvarious other gauging tools which may be desired to be utilized on thesurface plate l, in conjunction with the upright 8, and affords a meansof carrying out various gauging operations, all of which may be freefrom dimensional instability irrespective of temperature changes andother conditions.

Preferably the entire body of the upright frame 3 is formed of granitein order to resist any inaccuracies from temperature fluctuations. Itmay, however, be desired to form a part only of the upright of granite,with some other material utilized for the remainder of the tool. Variousother arrangements may be resorted to which utilize the property of thegranite of being free from dimensional instability.

A further modication of the invention has been illustrated in Figs. 5and 6, which disclose a straight edge member l5 also formed of anigneous rock such as granite, and including a straight edge surface I6,a rib portion I 1, and pedestals I8, with the rib portion I1 furtherbeing formed with openings I9. This tool conforms in all respects to theshape and style of a metal straight edge but is characterized by theproperties inherent in igneous rock as already set forth in connectionwith previous modications. Various other applications of igneous rockmay also be resorted to in accordance With the invention, a-s forexample in making ring gauges, plug gauges, buttons and anvils for snapgauges, and others. Any of the Various igneous rocks as a1- readyreferred to may be employed in this con nection.

From the foregoing, it will be seen that I have eiected substantialimprovements in gauges by means of which closer tolerance may beobtained, better resistance to wear is possible, freedom fromsubstantially all dimensional instability is achieved, and simplicityand cheapness are made possible in connection with precisioninstruments.

While I have shown a preferred embodiment of my invention, it should beunderstood that various changes and modifications may be resorted to, inkeeping with the spirit of the invention as defined by the appendedclaims.

I claim:

1. As an article of manufacture a gauge member which consists of a bodyportion and a gauging surface formed on the body portion, said bodyportion formed of granite and said gauging surface presenting amultiplicity of tiny irregularitiesl resulting from grinding the graniteat right angles to the head grain.

2. A gauge tool comprising a body of igneous rock which includes amultiplicity of very small particles arranged in a definite pattern toconstitute a head grain extending continuously from one side of theHoody to an opposite side along a denite axis, said tool presenting agauging surface which is dened by a plane cutting perpendicularly acrossthe said axis and intersecting two other sides of the body.

3. Means constituting a working surface for slidably engaging metalbodies, comprising a granite base material which includes a multiplicityof very small particles arranged in a deflnite pattern to constitute ahead grain which extends continuously from one side of the granite basematerial to an opposite side thereof along a definite axis, said granitematerial presenting a Working surface which is defined by a planecutting across the said axis substantially at right angles thereto.

JOHN B. HALL.

